The present invention relates to a label printer of the type used to print both human readable and machine readable indicia on labels from a strip of label stock and, more particularly, to such a printer in which the label stock has laterally extending perforation lines spaced along its length which define the individual labels and in which the leading label in the strip is printed and subsequently burst along the perforation line between it and the next label in the strip.
The printer of the present invention is particularly suited for weighing and labeling systems of the type used in supermarkets and grocery stores for determining the weight and total value of a random weight packaged item, printing a label including this information, and applying the label to the packaged item. Such a label may typically include machine readable bar code indicia, such as the Universal Product Code, specifying the type of product and the total cost of the labeled package, as well as human readable indicia specifying this information. Additional information such as weight, price per unit weight, and shelf life, may also be printed on the label in human readable indicia.
Each of a series of packages may be weighed and labeled automatically, as shown in Treiber U.S. Pat. No. 3,989,929, issued Nov. 2, 1976, and assigned to the assignee of the present invention. The Treiber patent discloses an arrangement by which a first human readable label is printed by one printer, and a second bar code label is printed by a second printer. The labels are then applied in succession to the top and bottom surfaces of a package. It will be appreciated, however, that it may be desirable to label packages with labels including both machine readable and human readable indicia.
Such labels may, for example, be printed on label stock consisting of a strip of release material carrying a plurality of labels mounted on the release material by a pressure sensitive adhesive. After printing labels of this type, they may be peeled from the strip of release material and applied to the packages. Although advantageous in certain respect, the use of pressure sensitive adhesive backed label stock is relatively expensive, and the labels are somewhat difficult to handle after being removed from the release material. Additionally, the web of release material takes up a substantial portion of the label stock supply space in the printer and, further, must be disposed of in some manner after the labels are printed and removed.
Other printers, such as shown for example in U.S. Pat. No. 3,104,806, issued Sept. 24, 1963, to Allen, and assigned to the assignee of the present invention, have utilized a strip of label stock having a heat activated adhesive coating which is softened by a heater in the printer output chute just prior to applying the labels to the packages. Heat activated adhesive backed label stock is advantageous in that no release material is required to support the labels during printing. Further, since the adhesive is not activated by heating until just prior to application of the labels, special label handling arrangements required with adhesive backed labels are unnecessary.
One difficulty, however, in printing on heat activated adhesive backed label stock and, indeed, upon any label stock not having a strip of backing material, is that printing typically must be accomplished on the label at the very forward end of the strip of label stock. If it is desired to print very close to the edge of the label, it may be difficult to engage the label on both sides of the printing station so as to hold it taut during printing.
In the printer disclosed in the Allen '806 patent printing is accomplished both prior to the detachment of the leading label from the label stock at a cutting station, and subsequent to the detachment of the leading label. It will be appreciated that while the label stock is not held on both sides of the print station during printing, nevertheless, the print quality of the human readable indicia produced by the Allen printer is acceptable. Although high resolution printing of human readable indicia is desirable, it is not critical so long as the printed indicia are legible. The resolution of printed machine readable indicia tends to be somewhat more important, however, since the printed bars must be well defined and accurately positioned for reliable reading by an optical reader system.
U.S. Pat. No. 4,057,015, issued Nov. 8, 1977, to Kodis, discloses a ticket printing system having a rotatable print drum with rows of raised printing elements disposed about its periphery. A print hammer assembly cooperates with each column of printing elements for printing indicia on a paper web advanced between the rotating drum and the hammer assembly. The web is pressed against specific printing elements by individual hammers. The Kodis system prints both bar codes and human readable indicia and the patent disclosure recognizes the need for high resolution. The Kodis printer prints both bar codes and human readable indicia on each ticket portion of the web prior to separation of that portion from the web and with the leading edge of the web being unsupported. An attempt is made to improve resolution in the Kodis printer by inking the print drum heavily. While this may produce bar codes which are of sufficient contrast, nevertheless, the bars may be slightly misplaced on the tickets since the tickets are supported only along their trailing edges during printing. In reading UPC characters, it is extremely important to provide accurate spacing between successive bar characters in order for the code information to be read successfully by machine.
A further problem which is encountered with printers of the type shown in the Kodis '015 and Allen '806 patents is that of separating the leading label or ticket from the balance of the label stock or paper web. Quite typically, as shown in both of these patents, a cutter arrangement is provided to detach the printed label or ticket from the unprinted stock or web. Such arrangements add appreciably to the complexity and cost of the printers. Additionally, cutting successive labels from the label stock produces paper dust which may contaminate various printer elements and require frequent cleaning.
Accordingly, it is seen that there is a need for a printing device capable of high resolution printing of both human readable indicia and machine readable indicia on the leading label in a strip of label stock, and for such a device in which the leading label may be separated from the strip of label stock subsequent to printing without unduly complicating the printer.